Process for producing hydrocarbon oil and system for producing hydrocarbon oil

ABSTRACT

Hydrocarbon oil obtained by Fischer-Tropsch synthesis reaction using a slurry bed reactor holding a slurry of a liquid hydrocarbon in which a catalyst is suspended; the hydrocarbon oil is fractionated into a distilled oil and a column bottom oil containing the catalyst fine powder by a rectifying column; at least part of the column bottom oil is transferred to a storage tank, and the catalyst fine powder is sedimented to the bottom of the storage tank to capture the catalyst fine powder; a residue of the column bottom oil is transferred from the rectifying column to a hydrocracker, and/or the supernatant of the column bottom oil from which the catalyst fine powder is captured by the storage tank is transferred from the storage tank to the hydrocracker; and using the hydrocracker, the residue of the column bottom oil and/or the supernatant of the column bottom oil is hydrocracked.

This application is a Divisional of U.S. patent application Ser. No.13/817,247, which is a National Stage of International Application No.PCT/JP2011/068481, filed Aug. 12, 2011, which claims priority toJapanese Application No. 2010-184085, filed Aug. 19, 2010. Thedisclosures of U.S. patent application Ser. No. 13/817,247 andPCT/JP2011/068481 are expressly incorporated by reference herein intheir entireties.

TECHNICAL FIELD

The present invention relates to a method for producing a hydrocarbonoil and a system for producing a hydrocarbon oil.

BACKGROUND ART

Recently, from the viewpoint of reduction in environmental load, cleanand eco-friendly liquid fuels in which the contents of sulfur andaromatic hydrocarbons are small have been demanded. From such aviewpoint, as a technique for producing a raw material hydrocarbon inorder to produce a fuel oil base material that contains no sulfur oraromatic hydrocarbons and is rich in aliphatic hydrocarbons,particularly, a kerosene and light oil base material, a method using aFischer-Tropsch synthesis reaction (hereinafter, referred to as the “FTsynthesis reaction” in some cases) in which carbon monoxide gas andhydrogen gas are used as the raw material has been examined.

Moreover, a technique in which a synthesis gas whose principal componentis carbon monoxide gas and hydrogen gas is produced by reforming of agaseous hydrocarbon raw material such as natural gas, a hydrocarbon oil(hereinafter, referred to as the “FT synthetic oil” in some cases) issynthesized from the synthesis gas by the FT synthesis reaction, andfurther, through an upgrading step that is a step of hydrogenating andrefining the FT synthetic oil to produce a variety of liquid fuel oilbase materials, the kerosene and light oil base material and naphtha orwax and the like are produced is known as a GM (Gas To Liquids) process(see the following Patent Literature 1, for example.).

As a synthesis reaction system that synthesizes the hydrocarbon oil bythe FT synthesis reaction, for example, a bubble column type slurry bedFT synthesis reaction system that blows a synthesis gas into a slurry,in which a solid catalyst (hereinafter, referred to as the “FT synthesiscatalyst” in some cases) particle having activity to the FT synthesisreaction is suspended in the hydrocarbon oil, to make the FT synthesisreaction is disclosed (see Patent Literature 2.).

As a bubble column type slurry bed FT synthesis reaction system, forexample, an external circulating system including a reactor thataccommodates a slurry to make the FT synthesis reaction, a gas feederthat blows the synthesis gas into a bottom of the reactor, an outflowpipe that evacuates from the reactor the slurry containing thehydrocarbon oil obtained by the FT synthesis reaction within thereactor, a catalyst separator that separates the slurry evacuatedthrough the outflow pipe into the hydrocarbon oil and the FT synthesiscatalyst particle, and a re-introducing pipe that re-introduces the FTsynthesis catalyst particle and part of the hydrocarbon oil separated bythe catalyst separator into the reactor is known.

CITATION LIST Patent Literature

[Patent Literature 1] Japanese Patent Application Laid-Open PublicationNo. 2004-323626

[Patent Literature 2] U.S. Patent Application Laid-Open Publication No.2007/0014703

SUMMARY OF INVENTION Technical Problem

The catalyst separator in the bubble column type slurry bed FT synthesisreaction system includes a filter whose opening is approximately 10 μm,for example. The FT synthesis catalyst particle in the slurry iscaptured by the filter to be separated from the hydrocarbon oil.

However, part of the FT synthesis catalyst particles are graduallyreduced to a fine powder due to friction between the FT synthesiscatalyst particles, friction with an inner wall or the like of thereactor, or thermal damage caused by the FT synthesis reaction. The finepowder whose particle size becomes smaller than the size of the openingof the filter in the catalyst separator (hereinafter, referred to as the“catalyst fine powder” in some cases) may unintendedly pass through thefilter with the hydrocarbon oil to flow into a reaction system in theupgrading step of the FT synthetic oil. The flow of the catalyst finepowder into the reaction system causes deterioration in the catalystused in the reaction system, increase in pressure loss of the reactor,and further, reduction in quality of liquid fuel base materials andliquid fuel products. However, it is difficult to provide a filterhaving an opening smaller than the particle size of the catalyst finepowder in a flow path in which the FT synthetic oil obtained by the FTsynthesis reaction flows at a large flow rate, thereby to capture thecatalyst fine powder, because pressure loss in the filter is large, andthe pressure loss is further increased by capturing of the catalyst finepowder.

The present invention has been made in consideration of the problemsabove, and an object of the present invention is to provide a method forproducing a hydrocarbon oil and a production system that can suppress aflow of a catalyst fine powder derived from a catalyst to be used forthe FT synthesis reaction into a reaction system in an upgrading step.

Solution to Problem

In order to achieve the object above, a method for producing ahydrocarbon oil according to the present invention comprises: a step ofobtaining a hydrocarbon oil containing a catalyst fine powder derivedfrom a catalyst by a Fischer-Tropsch synthesis reaction using a slurrybed reactor holding a slurry containing a liquid hydrocarbon and thecatalyst suspended in the liquid hydrocarbon within the slurry bedreactor; a step of fractionating the hydrocarbon oil into at least onedistilled oil and a column bottom oil containing the catalyst finepowder using a rectifying column; a step of transferring at least partof the column bottom oil to a storage tank, and sedimenting the catalystfine powder to a bottom of the storage tank to capture the catalyst finepowder; and a step of transferring a residue of the column bottom oilfrom the rectifying column to a hydrocracker, and/or transferring asupernatant of the column bottom oil in which the catalyst fine powderis captured in the storage tank from the storage tank to thehydrocracker to hydrocrack the residue of the column bottom oil and/orthe supernatant of the column bottom oil using the hydrocracker.

According to the method for producing a hydrocarbon oil according to thepresent invention, the catalyst fine powder contained in the FTsynthetic oil is condensed in the column bottom oil of the rectifyingcolumn, at least part of the column bottom oil in which the catalystfine powder is condensed is transferred to the storage tank, and thecatalyst fine powder is sedimented to the bottom of the storage tank tobe captured; thereby, the flow of the catalyst fine powder into areaction system (hydrocracker) for hydrocracking of the column bottomoil can be efficiently suppressed.

In the method for producing a hydrocarbon oil according to the presentinvention, it is preferable that the storage tank include a structurefor suppressing movement of the catalyst fine powder sedimented to thebottom of the storage tank in the bottom of the storage tank. Thereby,the flow of the catalyst fine powder into the reaction system(hydrocracker) for hydrocracking of the column bottom oil can be moreefficiently suppressed.

A system for producing a hydrocarbon oil according to the presentinvention includes: a Fischer-Tropsch synthesis reaction apparatus forobtaining a hydrocarbon oil containing a catalyst fine powder derivedfrom a catalyst, the apparatus having a slurry bed reactor holding aslurry containing a liquid hydrocarbon and the catalyst suspended in theliquid hydrocarbon within the slurry bed reactor; a rectifying columnfor fractionating the hydrocarbon oil at least one distilled oil and acolumn bottom oil; a hydrocracker for hydrocracking the column bottomoil; a bypass line connecting a column bottom of the rectifying columnto the hydrocracker; a transfer line branched from a branching point ofthe bypass line; and a storage tank that is connected to the transferline, and in which the catalyst fine powder is sedimented to a bottom tobe captured.

The system for producing a hydrocarbon oil according to the presentinvention can implement the method for producing a hydrocarbon oilaccording to the present invention.

In the system for producing a hydrocarbon oil according to the presentinvention, it is preferable that the storage tank include a structurefor suppressing movement of the catalyst fine powder sedimented to thebottom of the storage tank in the bottom of the storage tank. Thereby,the flow of the catalyst fine powder into a reaction system(hydrocracker) for hydrocracking of the column bottom oil can be moreefficiently suppressed.

Advantageous Effects of Invention

The present invention can provide a method for producing a hydrocarbonoil and a production system that can efficiently suppress the flow ofthe catalyst fine powder derived from the catalyst to be used for the FTsynthesis reaction into the reaction system in the upgrading step of theFT synthetic oil.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an example of a system for producing ahydrocarbon oil according to an embodiment of the present invention.

FIGS. 2(A), 2(B), 2(C), 2(D), 2(E), 2(F), and 2(G) each are a schematicview showing a specific example of a structure in the bottom of astorage tank that the system for producing a hydrocarbon oil accordingto the embodiment of the present invention includes.

FIGS. 3(A), 3(B), and 3(C) each are a schematic view showing a specificexample of an arrangement of a storage tank that the system for ahydrocarbon oil according to the embodiment of the present inventionincludes.

FIGS. 4(A) and 4(B) are a schematic view showing a specific example ofan arrangement of a storage tank that a system for a hydrocarbon oilaccording to the embodiment of the present invention includes.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to FIGS. 1 to 4, a method for producing ahydrocarbon oil using a system for producing a hydrocarbon oil and aproduction system according to one embodiment of the present inventionwill be described in detail. Same reference numerals will be given tosame or identical components.

Outline of System for Producing Hydrocarbon Oil

A system 100 for producing a hydrocarbon oil used in the presentembodiment is a plant facility for performing a GTL process thatconverts a hydrocarbon raw material such as natural gas into a liquidfuel (hydrocarbon oil) base material such as light oil, kerosene, andnaphtha. The system 100 for producing a hydrocarbon oil according to thepresent embodiment mainly includes a reformer (not shown), a bubblecolumn type slurry bed reactor C2, a first rectifying column C4, bypasslines L12 and L16, transfer lines L14 a and L14 b (or only L14 a in somecases), a storage tank T2, a hydrocracker C6, an intermediate fractionhydrorefining apparatus C8, a naphtha fraction hydrorefinig apparatusC10, and a second rectifying column C12. The line L12 that forms thebypass line connects the first rectifying column C4 to a mixing drum D6.The line L16 that forms the bypass line connects a mixing drum D2 to thehydrocracker C6. In FIG. 1, an example in which in the system 100 forproducing a hydrocarbon oil, the storage tank T2 is provided between thetransfer lines L14 a and L14 b has been shown; the storage tank T2 maybe connected to the transfer line L14 a, and the production system 100may not have the transfer line L14 b. In this case, at least part of thecrude wax fraction containing the catalyst fine powder flowed from thecolumn bottom of the first rectifying column C4 is fed through thetransfer line L14 a to the storage tank T2, and the supernatant of thecrude wax fraction in which the catalyst fine powder is captured in thestorage tank T2 is flowed reversely in the transfer line L14 a to bedischarged. The “line” means a piping for transferring a fluid.

Outline of Method for Producing Hydrocarbon Oil

A method for producing a hydrocarbon oil using the production system 100comprises the following steps S1 to S9.

In Step S1, in the reformer (not shown), natural gas as the hydrocarbonraw material is reformed to produce a synthesis gas containing carbonmonoxide gas and hydrogen gas.

In Step S2, in the bubble column type slurry bed reactor C2, by the FTsynthesis reaction using an FT synthesis catalyst, a hydrocarbon oil (FTsynthetic oil) is synthesized from the synthesis gas obtained in StepS1. In Step S2, a catalyst fine powder may be produced from part of theFT synthesis catalyst, and part of the catalyst fine powder may passthrough the filter, which separates the hydrocarbon oil from the FTsynthesis catalyst particles, to be mixed in the FT synthetic oil to befed to Step S3 described below.

In Step S3, in the first rectifying column C4, the FT synthetic oilobtained in Step S2 is fractionated into at least one distilled oil anda column bottom oil containing the catalyst fine powder. In the presentembodiment, by the fractionation, the FT synthetic oil is separated intoa crude naphtha fraction, a crude intermediate fraction, and a crude waxfraction. Here, the crude naphtha fraction and crude intermediatefraction are distilled oils each obtained by condensing a product oncevaporized from the FT synthetic oil in the first rectifying column C4,and evacuating the products from the column top of the first rectifyingcolumn C4 and the column middle thereof, respectively; the crude waxfraction is a column bottom oil evacuated as it is a liquid from thecolumn bottom without vaporization from the FT synthetic oil. The columnbottom oil may contain the catalyst fine powder produced in Step S2 andmixed in the FT synthetic oil. The crude naphtha fraction, the crudeintermediate fraction, and the crude wax fraction each refer to afraction obtained by fractionation of the FT synthetic oil and notsubjected to a hydrorefining or hydrocracking treatment.

The steps subsequent to Step S4 to be described below comprise theupgrading step of the FT synthetic oil.

In Step S4, at least part of the crude wax fraction that is the columnbottom oil of the first rectifying column C4 separated in Step S3 andcontains the catalyst fine powder is transferred through the line L12and the transfer line L14 a branched from the branching point of theline L12 to the storage tank T2; in the storage tank T2, the catalystfine powder contained in the crude wax fraction are sedimented to thebottom of the storage tank T2 to be separated and captured; thereby, thecatalyst fine powder is removed from the crude wax fraction.

In Step S5, of the crude wax fraction containing the catalyst finepowder and separated in Step S3, the remaining crude wax fraction nottransferred to the storage tank T2 in Step S4 is transferred through thelines L12 and L16 that form a bypass line from the first rectifyingcolumn C4 to the hydrocracker C6. The supernatant of the crude waxfraction in which in the storage tank T2, the catalyst fine powder issedimented and separated to be captured at the bottom of the storagetank T2 is transferred through the transfer line L14 b (or the line L14a in some cases) and the line L 16 from the storage tank T2 to thehydrocracker C6.

In Step S6, in the hydrocracker C6, the crude wax fraction separated inStep 3, subjected to removal of the catalyst fine powder from at leastpart of the crude wax fraction in Step S4, and transferred in Step S5 ishydrocracked.

In Step S7, in the intermediate fraction hydrorefining apparatus C8,hydrorefining of the crude intermediate fraction is performed.

In Step S8, in the naphtha fraction hydrorefining apparatus C10,hydrorefining of the crude naphtha fraction is performed. Further, thehydrorefined naphtha fraction is fractionated in a naphtha stabilizerC14 to recover naphtha (GTL-naphtha) that is a product of the GTLprocess.

In Step S9, a mixture of the hydrocracking product of the crude waxfraction and the hydrorefined product of the crude intermediate fractionis fractionated in the second rectifying column C12. By thefractionation, a light oil (GTL-light oil) base material and a kerosene(GTL-kerosene) base material that are products of the GTL process arerecovered.

Hereinafter, Steps S1 to S9 will be described more in detail.

Step S1

In Step S1, first, a sulfur compound contained in natural gas is removedby a desulfurization apparatus (not shown). Usually, the desulfurizationapparatus includes a hydrogenation desulfurization reactor filled with aknown hydrogenation desulfurization catalyst and an adsorptivedesulfurization apparatus provided at the rear stage thereof and filledwith an adsorptive material for hydrogen sulfide such as zinc oxide. Thenatural gas is fed to the hydrogenation desulfurization reactor withhydrogen, and the sulfur compound in the natural gas is converted intohydrogen sulfide. Subsequently, in the adsorptive desulfurizationapparatus, hydrogen sulfide is removed by adsorption, and the naturalgas is desulfurized. By the desulfurization of the natural gas,poisoning of a reforming catalyst filled in the reformer, the FTsynthesis catalyst used in Step S2, and the like by the sulfur compoundis prevented.

The desulfurized natural gas is fed to reforming using carbon dioxideand steam in the reformer to produce a synthesis gas at a hightemperature containing carbon monoxide gas and hydrogen gas as principalcomponents. The reforming reaction of the natural gas in

Step S1 is represented by reaction equations (1) and (2). The reformingmethod is not limited to the steam carbon dioxide gas reforming methodusing carbon dioxide and steam; for example, a steam reforming method, apartial oxidation reforming method (PDX) using oxygen, an autothermalreforming method (ATR) that is a combination of the partial oxidationreforming and the steam reforming method, a carbon dioxide gas reformingmethod, or the like can also be used.

CH₄+H₂O—>CO+3H₂   (1)

CH₄+CO₂—>2CO+2H₂   (2)

Step S2

In Step S2, the synthesis gas produced in Step Si is fed to the bubblecolumn type slurry bed reactor C2, and hydrocarbon is synthesized fromhydrogen gas and carbon monoxide gas in the synthesis gas.

The bubble column type slurry bed FT reaction system including thebubble column type slurry bed reactor C2 mainly includes the bubblecolumn type slurry bed reactor C2 that accommodates a slurry containingthe FT synthesis catalyst, a gas feeder that blows the synthesis gasinto the bottom of the reactor (not shown), a line L2 that evacuates thegaseous hydrocarbon obtained by the FT synthesis reaction and thenon-reacted synthesis gas from the column top of the bubble column typeslurry bed reactor C2, a gas liquid separator D2 that cools the gaseoushydrocarbon and non-reacted synthesis gas evacuated from the line L2 andseparates them into gas and liquid, an outflow pipe L6 that evacuatesthe slurry containing hydrocarbon oil from the reactor, a catalystseparator D4 that separates the slurry evacuated through the outflowpipe into the hydrocarbon oil and the FT synthesis catalyst particles,and a re-introducing pipe L10 that re-introduces the FT synthesiscatalyst particles and part of the hydrocarbon oil separated by thecatalyst separator D4 into the reactor, for example. Inside of thebubble column type slurry bed reactor C2, a heat conducting pipe (notshown) for removing the reaction heat generated by the FT synthesisreaction, through which cool water is flowed, is provided.

As the FT synthesis catalyst used in the bubble column type slurry bedreactor C2, a known carrier type FT synthesis catalyst in which anactive metal is supported by an inorganic carrier is used. As theinorganic carrier, porous oxides such as silica, alumina, titania,magnesia, and zirconia are used; silica or alumina is preferable, andsilica is more preferable. Examples of the active metal include cobalt,ruthenium, iron, and nickel; cobalt and/or ruthenium is preferable, andcobalt is more preferable. The amount of the active metal to besupported is preferably 3 to 50% by mass, and more preferably 10 to 40%by mass based on the mass of the carrier. In the case where the amountof the active metal to be supported is less than 3% by mass, theactivity tends to be insufficient; in the case where the amount of theactive metal to be supported is more than 50% by mass, the activitytends to be reduced by aggregation of the active metal. Other than theactive metal, other components may be supported in the FT synthesiscatalyst in order to improve the activity or control the number ofcarbon atoms of hydrocarbon to be produced and distribution thereof.Examples of the other component include a compound containing a metalelement such as zirconium, titanium, hafnium, sodium, lithium, andmagnesium. It is preferable that the average particle size of the FTsynthesis catalyst particle be 40 to 150 μm so that the catalystparticles may easily flow within the slurry bed reactor as a slurrysuspended in the liquid hydrocarbon. It is also preferable that from theviewpoint of the fluidity as the slurry, the shape of the FT synthesiscatalyst particle be spherical.

The active metal is supported by the carrier by a known method. Examplesof the compound containing the active metal element used for supportingcan include salts of mineral acid of the active metal such as nitricacid salts, hydrochloric acid salts, and sulfuric acid salts; salts oforganic acid such as formic acid, acetic acid, and propionic acid; andcomplexes such as acetylacetonate complexes. The supporting method isnot particularly limited, and an impregnation method represented by anIncipient Wetness method using a solution of a compound containing theactive metal element is preferably used. The carrier by which thecompound containing the active metal element is supported is dried by aknown method, and more preferably fired under an air atmosphere by aknown method. The firing temperature is not particularly limited, andusually approximately 300 to 600° C. By the firing, the compoundcontaining the active metal element on the carrier is converted intometal oxide.

For the FT synthesis catalyst in order to demonstrate high activity tothe FT synthesis reaction, it is necessary that the active metal atom beconverted into a metal by reduction treatment of the catalyst in whichthe active metal atom is oxidized. The reduction treatment is usuallyperformed by contacting the catalyst with reducing gas under heating.Examples of the reducing gas include hydrogen gas, gases containinghydrogen gas such as a mixed gas of hydrogen gas and an inert gas suchas nitrogen gas, and carbon monoxide gas; preferable is hydrogencontaining gas, and more preferable is hydrogen gas. The temperature inthe reduction treatment is not particularly limited, and it ispreferable that it be usually 200 to 550° C. At a reduction temperatureless than 200° C., the active metal atom tends not to be sufficientlyreduced and not to sufficiently demonstrate the catalyst activity; at atemperature more than 550° C., the catalyst activity tends to be reduceddue to aggregation of the active metal or the like. The pressure in thereduction treatment is not particularly limited, and it is preferablethat it be usually 0.1 to 10 MPa. At a pressure less than 0.1 MPa, theactive metal atom tends not to be sufficiently reduced and not tosufficiently demonstrate the catalyst activity; at a pressure more than10 MPa, facility cost tends to be increased for a need to increasepressure resistance of the apparatus. The time of the reductiontreatment is not particularly limited, and it is preferable that it beusually 0.5 to 50 hours. At a reduction time less than 0. 5 hours, theactive metal atom tends not to be sufficiently reduced and not tosufficiently demonstrate the catalyst activity; at a reduction time morethan 50 hours, the catalyst activity tends to be reduced due toaggregation of the active metal or the like, and the efficiency tends tobe reduced. The facility in which the reduction treatment is performedis not particularly limited; for example, the reduction treatment may beperformed in the absence of liquid hydrocarbon within the reactor toperform the FT synthesis reaction. The reduction treatment may also beperformed within a facility connected to the reactor to perform the FTsynthesis reaction, and the catalyst may be transferred through a pipingto the reactor to perform the FT synthesis without contacting thecatalyst with the air.

On the other hand, in the case where the reduction treatment isperformed in a facility located in a place different from that of thefacility to perform the FT synthesis reaction such as a catalystproduction facility, the catalyst activated by the reduction treatmentis deactivated if the catalyst is contacted with the air duringtransportation or the like. In order to prevent this deactivation, it ispreferable that the activated catalyst is subjected to a stabilizationtreatment. Examples of the stabilization treatment include a method forperforming a light oxidation treatment on an activated catalyst to forman oxidation coating on the surface of an active metal so as not tofurther progress oxidation due to contact with the air, or a method forcoating an activated catalyst with hydrocarbon wax or the like in theabsence of the air to block contact with the air. In the method forforming the oxidation coating, the catalyst can be fed to the FTsynthesis reaction as it is after transportation; in the method forperforming coating with wax or the like, when the catalyst is suspendedin a liquid hydrocarbon to form a slurry, the wax or the like used forcoating is dissolved in liquid hydrocarbon, and the activity isdemonstrated.

The reaction condition on the FT synthesis reaction in the bubble columntype slurry bed reactor C2 is not limited; for example, the followingreaction condition is selected. Namely, it is preferable that thereaction temperature be 150 to 300° C. from the viewpoint of increase inthe conversion rate of carbon monoxide and the number of carbon atoms ofhydrocarbon to be produced. It is preferable that the reaction pressurebe 0.5 to 5.0 MPa. It is preferable that a hydrogen/carbon monoxideratio (molar ratio) in the raw material gas be 0.5 to 4.0. It isdesirable that the conversion rate of carbon monoxide be not less than50% from the viewpoint of the production efficiency of the FT syntheticoil.

Inside of the bubble column type slurry bed reactor C2, a slurry inwhich the FT synthesis catalyst particles are suspended in the liquidhydrocarbon (preferably the product of the FT synthesis reaction) isaccommodated. The synthesis gas (CO and H₂) obtained in Step S1 isinjected into the slurry within the reactor through a dispersion plateinstalled in the bottom of the bubble column type slurry bed reactor C2.The synthesis gas blown into the slurry becomes bubbles, which moveupward in the slurry to the upper portion of the bubble column typeslurry bed reactor C2. In the course thereof, the synthesis gas isdissolved in the liquid hydrocarbon to contact the FT synthesis catalystparticles; thereby, the FT synthesis reaction progresses to producehydrocarbon. The FT synthesis reaction is represented by reactionequation (3) below, for example.

2nH₂+nCO—>(—CH₂—)_(n)+nH₂O   (3)

A gaseous phase exists in the upper portion of the slurry accommodatedin the bubble column type slurry bed reactor C2. The light hydrocarbonthat is produced by the FT synthesis reaction and gaseous under thecondition within the bubble column type slurry bed reactor C2 and thenon-reacted synthesis gas (CO and H₂) move from the slurry phase to thegaseous phase portion, and are further evacuated from the top of thebubble column type slurry bed reactor C2 through the line L2. Then, bythe gas liquid separator D2 including a cooler (not shown) and connectedto the line L2, the evacuated light hydrocarbon and the non-reactedsynthesis gas are separated into the gas content containing thenon-reacted synthesis gas and hydrocarbon gas having C₄ or less asprincipal components and a liquid hydrocarbon (light hydrocarbon oil)liquefied by cooling. Of these, the gas content is recycled to thebubble column type slurry bed reactor C2, and the non-reacted synthesisgas contained in the gas content is fed to the FT synthesis reactionagain. On the other hand, the light hydrocarbon oil is fed through aline L4 and a line L8 to the first rectifying column C4.

On the other hand, the hydrocarbon (heavy hydrocarbon oil) that isproduced by the FT synthesis reaction and a liquid under the conditionwithin the bubble column type slurry bed reactor C2 and the slurrycontaining the FT synthesis catalyst particles are fed from the centralportion of the bubble column type slurry bed reactor C2 through the lineL6 to the catalyst separator D4. The FT synthesis catalyst particles inthe slurry are captured by the filter installed within the catalystseparator D4. The heavy hydrocarbon oil in the slurry passes through thefilter to be separated from the FT synthesis catalyst particles, and isevacuated from the line L8 to merge with the light hydrocarbon oil fromthe line L4. The mixture of the heavy hydrocarbon oil and the lighthydrocarbon oil is heated in a heat exchanger H2 installed halfway ofthe line L8, and then fed to the first rectifying column C4.

As the product of the FT synthesis reaction, the hydrocarbon (lighthydrocarbon) that is gaseous under the condition within the bubblecolumn type reactor C2 and the hydrocarbon (heavy hydrocarbon oil) thatis a liquid under the condition within the bubble column type reactor C2are obtained. These hydrocarbons are substantially normal paraffin, andfew aromatic hydrocarbon, naphthene hydrocarbon and isoparaffin arecontained. Distribution of the number of carbon atoms of the lighthydrocarbon and heavy hydrocarbon oil in total widely ranges from C₄ orless as a gas at normal temperature to approximately C_(go), forexample, as a solid (wax) at room temperature. The reaction product alsocontains olefins and oxygen-containing compounds containing oxygen atomsderived from carbon monoxide (e.g., alcohols) as a by-product.

If the opening of the filter that the catalyst separator D4 includes issmaller than the particle size of the FT synthesis catalyst particle,the size of the opening is not particularly limited, preferably 10 to 20μm, and more preferably 10 to 15 μm. The FT synthesis catalyst particlescaptured by the filter that the catalyst separator D4 includes arere-introduced through the line L10 into the bubble column type reactorC2 by properly flowing (backwashing) the liquid hydrocarbon in adirection opposite to the ordinary flow direction, and re-used.

Part of the FT synthesis catalyst particles that flow as the slurry inthe bubble column type slurry bed reactor C2 wear or collapse due tofriction between the catalyst particles, friction with the wall of theapparatus or the heat conducting pipe provided within the reactor forcooling, or damages or the like caused by the reaction heat to producethe catalyst fine powder. Here, the particle size of the catalyst finepowder is not particularly limited, and is a size such that the catalystfine powder may pass through the filter that the catalyst separator D4includes, namely, the particle size is equal to or smaller than the sizeof the opening of the filter. For example, in the case where the openingof the filter is 10 μm, a catalyst particle having a particle size ofnot more than 10 μm is referred to as the catalyst fine powder. Thecatalyst fine powder contained in the slurry passes through the filterwith the heavy hydrocarbon oil, and fed to the first rectifying columnC4.

Step S3

In Step S3, the hydrocarbon oil comprising the mixture of the lighthydrocarbon oil and heavy hydrocarbon oil fed from the bubble columntype slurry bed reactor C2 (FT synthetic oil) is fractionated in thefirst rectifying column C4. By the fractionation, the FT synthetic oilis separated into the crude naphtha fraction having approximately C₅ toC₁₀ whose boiling point is lower than approximately 150° C., the crudeintermediate fraction having approximately C₁₁ to C₂₀ whose boilingpoint is approximately 150 to 360° C., and the crude wax fraction havingapproximately C₂₁ or more whose boiling point is approximately more than360° C.

The crude naphtha fraction is evacuated through a line L20 connected tothe column top of the first rectifying column C4. The crude intermediatefraction is evacuated through a line L18 connected to the centralportion of a first rectifying column C4. The crude wax fraction isevacuated through the line L12 connected to the bottom of the firstrectifying column C4.

The catalyst fine powder contained in the FT synthetic oil to be fed tothe first rectifying column C4 does not accompany the distilled oilobtained by vaporization once and subsequent condensation within thefirst rectifying column C4 (crude naphtha fraction and crudeintermediate fraction), and substantially accompanies only the crude waxfraction that is not vaporized within the first rectifying column C4 butkept in a liquid state to become the column bottom oil.

Accordingly, the catalyst fine powder contained in the FT synthetic oil(the whole fractions) is to be condensed in the crude wax fraction.Thereby, specifically, in the step of capturing and removing thecatalyst fine powder described later, as the concentration of thecatalyst fine powder in the target crude wax fraction is increased, theamount of the liquid to be treated is reduced; accordingly, capturingand removal of the catalyst fine powder can be efficiently performed.

Step S4

In Step S4, at least part of the crude wax fraction separated in Step S3is transferred from the column bottom of the first rectifying column C4through the line L12 and the transfer line L14 a to the storage tank T2;in the storage tank T2, the catalyst fine powder contained in the crudewax fraction is sedimented to the bottom of the storage tank T2 andseparated from the crude wax fraction to be captured.

The line L12 connected to the column bottom of the first rectifyingcolumn C4 is connected to the mixing drum D6, and the mixing drum D6 andthe hydrocracker C6 are connected to each other through the line L16.The line L12 and line L16 through the mixing drum D6 form the bypassline. Here, the bypass line means a line connecting the column bottom ofthe first rectifying column C4 to the hydrocracker C6 without passingthrough the storage tank T2 for capturing and removing the catalyst finepowder from the crude wax fraction. The transfer line L14 a is branchedfrom the branching point on the line L12, and connected to the storagetank T2. The transfer line L14 b for discharging the supernatant of thecrude wax fraction, from which the catalyst fine powder is removed, fromthe storage tank T2 is connected to the line L12 downstream of thebranching point. As described above, it may be configured so that theproduction system 100 has no transfer line L14 b, and discharges thesupernatant of the crude wax fraction from the storage tank T2 using thetransfer line L14 a. It is preferable that the line L12 (preferably, theposition downstream of the branching point of the transfer line L14 aand upstream of a merging point of the transfer line L14 b) that formthe bypass line, the transfer line L14 a, and the transfer line L14 beach be provided with a flow meter and a valve for closing/opening theline and adjusting the flow rate.

In the example above, it is configured that the transfer line

L14 a is branched from the line L12; it may be configured that thetransfer line L14 a is branched from the line L16, and the transfer lineL14 b returns to the line L16. In this case, however, because thecatalyst fine powder contained in the crude wax fraction is diluted bythe column bottom oil (uncracked wax fraction) of the second rectifyingcolumn C12 recycled through the line L3 8, an effect of condensing thecatalyst fine powder in Step S3 is reduced; accordingly, it ispreferable that the transfer line L14 a be branched from the line L12,and returns to the line L12 as described above.

The storage tank T2 may be an ordinary storage tank (tank), and mayserve as a storage tank for temporarily storing the crude wax fractionin order to balance the outflow rate of the crude wax fraction separatedin Step S3 and the feeding rate of the crude wax fraction to thehydrocracker C6.

It is preferable that the bottom of the storage tank T2 include astructure for suppressing movement of the catalyst fine powdersedimented to the bottom thereof. The structure for suppressing movementof the catalyst fine powder sedimented to the bottom is one in which themovement or flow of the catalyst fine powder sedimented to the bottomand/or the crude wax fraction in the vicinity thereof is inhibitedgeometrically or by other mechanism, thereby to sediment the catalystfine powder once to the bottom of the storage tank T2 and suppressmovement (float) of the captured catalyst fine powder. Examples of sucha structure include a structure having a bottom plate or a depressionand a projection or a depression on the bottom plate in which thecatalyst fine powder is captured by the depression; a structure having apartition plate on a bottom plate in which the catalyst fine powder iscaptured in each segment defined by the partition plates; a structurehaving a three-dimensional mesh pattern structure on a bottom plate inwhich the catalyst fine powder is captured in a space formed by thepattern; a structure having a plate-like body installed above the bottomplate spaced from the bottom plate at a predetermined intervalapproximately parallel thereto and having an opening, in which thecatalyst fine powder passing through the opening is captured on thebottom plate; and a structure in which a magnetic material is arrangedin the bottom plate, and magnetic catalyst fine powder is captured.

Hereinafter, each of the structures of the bottom of the storage tank T2will be described more specifically with reference to FIG. 2.

Structure having Depression and Projection or Depression

Examples of the structure having a bottom plate or a depression and aprojection or a depression on the bottom plate in which the catalystfine powder is captured by the depression include a structure having acorrugated plate shown in FIG. 2(A). FIG. 2(A) shows an example in whicha corrugated plate 20 is installed on a flat bottom plate; the bottomplate of the storage tank T2 itself may have such a structure. Thecorrugated plate may cover the entire surface of the bottom plate. Thewidth (pitch) of repeating units, height of the corrugated shape and thelike of the corrugated plate are properly determined. The sedimentedcatalyst fine powder is captured by the depression of the corrugatedplate. Other examples of the structure having a bottom plate or adepression and a projection or a depression on the bottom plate in whichthe catalyst fine powder is captured by the depression include astructure having a depression 22 as shown in FIG. 2(B). FIG. 2(B) showsan example in which the shape of the depression is cylindrical, but theshape is not limited to this, and may be other shape, e.g., prismatic,semi-spherical, or the like. The size and depth of each depression, thenumber of the depressions, and the like are properly determined.

Structure having Partition Plate

Examples of the structure having a partition plate on the bottom platein which the catalyst fine powder is captured in each segment defined bythe partition plates include a structure as shown in FIG. 2(C). It ispreferable that a partition plate 24 be provided vertical to the bottomplate, but not limited to this. In FIG. 2(C), the partition plates areprovided parallel to each other on the bottom plate, but not limited tothis arrangement; examples thereof include an arrangement having alattice partition plate in a plan view that is a combination of thepartition plates parallel to each other shown in FIG. 2(C) withpartition plates intersecting perpendicular thereto; an arrangementhaving partition plates concentrically provided in a plan view; anarrangement having partition plates spirally provided in a plan view; anarrangement having partition plates provided radially from the center ina plan view; or an arrangement having partition plates in combinationthereof. Here, the height, interval, and the like of each partitionplate are arbitrarily determined.

Structure having Three-Dimensional Mesh Structure

Examples of the structure having a three-dimensional mesh patternstructure on the bottom plate in which the catalyst fine powder iscaptured in a space formed by the pattern include a structure in whichan entangled fibrous structure 26 is installed on the bottom plate, asshown in FIG. 2(D). The material that forms the structure may be thosecomprising a metal fiber such as entangled iron fibers (steel wire),woven fabrics and non-woven fabrics formed from a synthetic fiber havingheat resistance, or the like, for example. In these structures, spacesare formed between the entangled fibers, and the sedimented catalystfine powder is captured by the spaces, for example.

Structure having Plate-Like Body having Opening Above Bottom Plate

Examples of structure having a plate-like body installed above thebottom plate spaced from the bottom plate at a predetermined intervalapproximately parallel thereto and having an opening, in which thecatalyst fine powder passing through the opening is captured on thebottom plate include a structure having a mesh 28 above the bottom plateas shown in FIG. 2(E). The opening of the mesh is not particularlylimited as long as the catalyst fine powder can pass through theopening, and is determined depending on the balance between passibilityin sediment of the catalyst fine powder and an effect of suppressing thecatalyst fine powder once sedimented to the bottom plate passing throughthe mesh again to float above the mesh. Other examples of the structurehaving a plate-like body installed above the bottom plate spaced fromthe bottom plate at a predetermined interval approximately parallelthereto and having an opening, in which the catalyst fine powder passingthrough the opening is captured on the bottom plate include a structurehaving a plate-like body 30 above the bottom plate, the plate-like body30 having a funnel-shaped structure having an inclination from theperiphery toward the center and an opening in the center as shown inFIG. 2(F). FIG. 2(F) shows an example in which the plate-like bodyhaving one funnel-shaped structure covers the cross section of thestorage tank T2 in the horizontal direction, while the number of thefunnel-shaped structure may be plural. In that case, it is preferablethat the area in the horizontal portion between the funnel-shapedstructures be made as small as possible. The shape of the funnel-shapedstructure not only is conical, but also may be a polygonal pyramid suchas a quadrangular pyramid. The number of these funnel-shaped structures,an inclination of the inclined portion, the size of the opening, and thelike are properly determined.

The structures of the bottom of the storage tank T2 above are those inwhich the flow of the catalyst fine powder captured by sediment due toconvection of the crude wax in the vicinity thereof is geometricallyinhibited, or movement of the captured catalyst fine powder out of thesegments geometrically partitioned is inhibited even if the flow occurs,thereby to suppress discharging of the catalyst fine powder from thestorage tank T2 by “floating.”

Structure in which Magnetic Material is Arranged in Bottom Plate

Examples of the structure in which a magnetic material is provided inthe bottom plate, and magnetic catalyst fine powder is captured includea structure in which a magnetic body 32 such as a permanent magnet isprovided in the bottom plate, for example, as shown in FIG. 2(G). As theFT synthesis catalyst, a catalyst in which a magnetic metal such ascobalt, iron, and nickel as an active metal is supported by a carriersuch as silica is usually used. Accordingly, when the catalyst finepowder derived from the FT synthesis catalyst and having these metals issedimented to the bottom of the storage tank T2, the catalyst finepowder is adsorbed by a magnetic force of the magnetic body provided inthe bottom; then, movement thereof is suppressed even if the flow occursin the crude wax fraction in the vicinity thereof. The magnetic materialmay be an electromagnet other than the permanent magnet; in that case, asingle or a plurality of electromagnets are provided in the bottom ofthe storage tank T2, and an electric facility for generating magnetismin the electromagnet is installed; the electric facility is electricallyconducted when the catalyst fine powder is captured in the storage tankT2.

The structure for suppressing movement of the catalyst fine powdersedimented to the bottom of the storage tank T2 is not limited to theexamples above, and any structure that can suppress the movement or flowof the catalyst fine powder sedimented to the bottom of the storage tankT2 and/or the crude wax fraction in the vicinity thereof by the same orsimilar action and effect as or to those above can be used.

The transfer line L14 a, the transfer line L14 b, and the storage tankT2 may be composed of the corresponding individual lines and anindividual storage tank provided therebetween, or composed of aplurality of lines and storage tanks in which the transfer line L14 aand the transfer line L14 b each are branched into a plurality of linesparallel to each other, and each of the storage tanks is providedbetween these branched lines.

The capturing of the catalyst fine powder contained in the crude waxfraction in the storage tank T2 comprises: a transferring step oftransferring at least part of the crude wax fraction flowed from thecolumn bottom of the first rectifying column C4 to the storage tank T2,and a discharging step of discharging the supernatant obtained bysedimenting the catalyst fine powder in the crude wax fractiontransferred to the storage tank T2 from the storage tank T2; thetransferring step and the discharging step may be performed at the sametime. Alternatively, the discharging step may be performed after end ofthe transferring step. Further, a settling step of settling the crudewax fraction without performing transfer and discharge may be providedbetween the transferring step and the discharging step. In order tosecurely capture the catalyst fine powder in the crude wax fraction, itis preferable that capturing of the catalyst fine powder comprise thetransferring step, the settling step, and the discharging step in thisorder. A specific method for operation of these will be described later.

Step S5

In Step S5, of the crude wax fraction that is the column bottom of thefirst rectifying column oil C4 separated in Step S3 and contains thecatalyst fine powder, the remaining crude wax fraction not transferredto the storage tank T2 in Step S4 is transferred through the line L12and line L16 that form the bypass line from the first rectifying columnC4 to the hydrocracker C6, and/or the supernatant of the crude waxfraction in which the catalyst fine powder is captured by sediment atthe bottom in the storage tank T2 is transferred through the transferline L14 b (transfer line L14 a and line L12 in some cases) and the lineL16 from the storage tank T2 to the hydrocracker C6.

Next, a specific method will be described in which in Step S4 and StepS5, at least part of the crude wax fraction flowed from the columnbottom of the first rectifying column C4 is transferred to the storagetank T2 to capture the catalyst fine powder, and the supernatant of thecrude wax fraction in which the catalyst fine powder is captured and/orthe remaining crude wax fraction not transferred to the storage tank T2is transferred to the hydrocracker C6. It is preferable thathydrocracking of the crude wax fraction in the hydrocracker C6 (Step S6)be continuously performed; for that, in Step S5, transfer of the crudewax fraction through the bypass line and/or the transfer line L14 b(transfer line L14 a and line L12 in some cases) and the line L16 fromthe storage tank T2 to the hydrocracker C6 needs to be continuouslyperformed.

In the case where the storage tank T2 is composed of a single storagetank, at least part of the crude wax fraction flowed from the columnbottom of the first rectifying column may be transferred through theline L12 and the transfer line L14 a to the storage tank T2 (dischargingfrom the storage tank T2 is not performed at the same time.), and at thesame time, the remaining crude wax fraction may be transferred throughthe bypass line (line L12 and line L16) directly to the hydrocracker C6.In this case, after the crude wax fraction is transferred to the storagetank T2 or after settling is further performed, the supernatant fromwhich the catalyst fine powder is captured is discharged from thestorage tank T2, and transferred through the transfer line L14 b and theline L16 to the hydrocracker C6 (see FIG. 3(A)). In the case where thesystem 100 for producing a hydrocarbon oil has no transfer line L14 band has only the transfer line L14 a, the supernatant is dischargedusing the transfer line L14 a instead of the transfer line L14 b, andfurther transferred to the hydrocracker C6 through the line L12 and theline L16 (see FIG. 3(B)).

Alternatively, at least part of the crude wax fraction flowed from thecolumn bottom of the first rectifying column C4 may be transferredthrough the line L12 and the transfer line L14 a to the storage tank T2,and at the same time, the supernatant from which the catalyst finepowder is captured may be discharged from the storage tank T2 throughthe line L14 b, and further fed through the line L16 to the hydrocrackerC6 (see FIG. 3(C)). At this time, in the case where of the crude waxfraction flowed from the column bottom of the first rectifying columnC4, the remaining crude wax fraction not transferred to the storage tankT2 exists, the remaining crude wax fraction is fed through the bypassline (line L12 and line L16) to the hydrocracker C6.

In the case where the storage tank T2 is composed of two storage tanks(first storage tank and second storage tank) provided in parallel, thetwo storage tanks may be used by switching as below, for example.Namely, the crude wax fraction is transferred from the column bottom ofthe first rectifying column C4 to the first storage tank to be stored(discharging from the first storage tank is not performed at the sametime.). After transfer of the crude wax fraction to the first storagetank is completed, the supernatant of the crude wax fraction from whichthe catalyst fine powder is captured is discharged from the firststorage tank, and transferred through the transfer line L14 b and theline L16 to the hydrocracker C6; at the same time, the crude waxfraction is transferred from the column bottom of the first rectifyingcolumn C4 to the second storage tank to be stored (discharging from thesecond storage tank is not performed at the same time.). After transferof the crude wax fraction to the second storage tank is completed, thesupernatant of the crude wax fraction from which the catalyst finepowder is captured is discharged from the second storage tank, andtransferred through the transfer line L14 b and the line L16 to thehydrocracker C6; at the same time, this time, the crude wax fraction istransferred from the column bottom of the first rectifying column C4 tothe first storage tank to be stored. Hereinafter, in the same manner,the two storage tanks are switched, and transfer, storage, and dischargeare alternately repeated; thereby, the supernatant of the crude waxfraction from which the catalyst fine powder is captured can becontinuously fed to the hydrocracker C6 (see FIG. 4(A)). At this time,in the case where of the crude wax fraction flowed from the columnbottom of the first rectifying column C4, the remaining crude waxfraction not transferred to the storage tank T2 exists, the remainingcrude wax fraction is fed through the bypass line (line L12 and lineL16) to the hydrocracker C6.

In the case where the storage tank T2 is composed of three storage tanks(first storage tank, second storage tank, and third storage tank)provided in parallel, the three storage tanks may be used by switchingas below, for example. Namely, the crude wax fraction is transferred tothe first storage tank (transferring step); in the second storage tank,the crude wax fraction already transferred is settled and the catalystfine powder is sedimented (settling step); in the third storage tank,the supernatant of the crude wax fraction in which sediment andcapturing of the catalyst fine powder by settling are completed isdischarged, and transferred to the hydrocracker C6 (discharging step).Next, in the first storage tank in which transfer of the crude waxfraction is completed, the crude wax fraction is settled and thecatalyst fine powder is sedimented (settling step); in the secondstorage tank in which sediment and capturing of the catalyst fine powderby settling is completed, the supernatant of the crude wax fraction isdischarged, and transferred to the hydrocracker C6 (discharging step);the crude wax fraction is transferred from the column bottom of thefirst rectifying column C4 to the third storage tank in which dischargeof the supernatant is completed (transferring step). Hereinafter, in thesame manner, the three storage tanks are sequentially switched, thetransferring step, the settling step, and the discharging step arerepeated in the respective storage tanks; thereby, the crude waxfraction from which the catalyst fine powder is removed can becontinuously fed to the hydrocracker C6 (see FIG. 4(B)). At this time,in the case where of the crude wax fraction flowed from the columnbottom of the first rectifying column C4, the remaining crude waxfraction not transferred to the storage tank T2 exists, the remainingcrude wax fraction is fed through the bypass line (line L12 and lineL16) to the hydrocracker C6.

As described above, in the system 100 for producing a hydrocarbon oilaccording to the present invention, examples of the embodiment in whichthe storage tank T2 is composed of a single storage tank, two storagetanks provided in parallel, or three storage tanks provided in parallel,and examples of a preferable embodiment of Step S4 and Step S5 in themethod for producing a hydrocarbon oil according to the presentinvention in the respective cases have been described, but theembodiment will not be limited to these examples. For example, thestorage tank T2 may be composed of four or more storage tanks providedin parallel, a plurality of storage tanks arrange in serial, or three ormore storage tanks in parallel and in serial. Moreover, the embodimentof Step S4 and Step S5 in the method for producing a hydrocarbon oilaccording to the present invention is not particularly limited as longas the crude wax fraction flowed from the column bottom of the firstrectifying column C4 is continuously fed through the bypass line and/orthe discharging line from the storage tank T2 to the hydrocracker C6,and the catalyst fine powder is captured in the storage tank T2.

Step S6

In Step S6, the supernatant of the crude wax fraction transferred fromthe storage tank T2 through the transfer line L14 b (transfer line L14 aand line L12 in some cases) and the line L16 to the hydrocracker C6,from which the catalyst fine powder is captured in the storage tank T2in Step S5, and/or the crude wax fraction transferred from the columnbottom of the first rectifying column C4 through the bypass line (linesL12 and L16) to the hydrocracker C6, from which the catalyst fine powderis not removed, is hydrocracked in the hydrocracker C6.

The crude wax fraction transferred by Step S5, with hydrogen gas fed bya feed line of the hydrogen gas connected to the line L16 (not shown),is heated to a temperature needed for hydrocracking of the crude waxfraction by a heat exchanger H4 provided in the line L16, and then fedto the hydrocracker C6 to be hydrocracked. The crude wax fraction notsufficiently hydrocracked in the hydrocracker C6 (hereinafter, referredto as the “uncracked wax fraction” in some cases) is recovered as thecolumn bottom oil of the second rectifying column C12 in Step S9,recycled by a line L38 to the line L12, mixed with the crude waxfraction from the first rectifying column C4 and/or the storage tank T2in the mixing drum D6, and fed to the hydrocracker C6 again.

The type of the hydrocracker C6 is not particularly limited, and a fixedbed flow reactor filled with a hydrocracking catalyst is preferablyused. The reactor may be singular, or a plurality of reactors may beprovided in serial or in parallel. Moreover, the catalyst bed within thereactor may be singular or plural.

As the hydrocracking catalyst filled in the hydrocracker C6, a knownhydrocracking catalyst is used, and a catalyst in which a metal that hashydrogenation activity and belongs to Group 8 to Group 10 in theperiodic table of the elements is supported by an inorganic carrierhaving a solid acidity is preferably used.

Examples of the inorganic carrier that forms the hydrocracking catalystand has suitable solid acidity include those comprising crystallinezeolite such as ultra stable Y-type (USY) zeolite, Y-type zeolite,mordenite, and 13 zeolite, and one or more inorganic compounds selectedfrom amorphous composite metal oxides having heat resistance such assilica alumina, silica zirconia, and alumina boria. Further, as thecarrier, compositions comprising USY zeolite and one or more amorphouscomposite metal oxides selected from silica alumina, alumina boria, andsilica zirconia are more preferable, and compositions comprising USYzeolite and alumina boria and/or silica alumina are still morepreferable.

USY zeolite is the one obtained by ultra-stabilizing Y-type zeolite by ahydrothermal treatment and/or acid treatment; in addition to the microfine porous structure called micro fine pores that Y-type zeoliteoriginally has and whose pore size is not more than 2 nm, new fine poreshaving a pore size in the range of 2 to 10 nm are formed in USY zeolite.The average particle size of USY zeolite is not particularly limited,preferably not more than 1.0 μm, and more preferably not more than 0.5μm. Moreover, in USY zeolite, it is preferable that the molar ratio ofsilica/alumina (molar ratio of silica to alumina) be 10 to 200, and itis more preferable that the molar ratio be 15 to 100, and it is stillmore preferable that the molar ratio be 20 to 60.

Moreover, it is preferable that the carrier contain 0.1 to 80% by massof crystalline zeolite and 0.1 to 60% by mass of amorphous compositemetal oxide having heat resistance.

The carrier can be produced as follows: a carrier composition comprisingthe inorganic compound having solid acidity and a binder is molded, andfired. The proportion of the inorganic compound having solid acidity tobe blended is preferably 1 to 70% by mass, and more preferably 2 to 60%by mass based on the whole mass of the carrier. Moreover, in the casewhere the carrier contains USY zeolite, the proportion of USY zeolite tobe blended is preferably 0.1 to 10% by mass, and more preferably 0.5 to5% by mass based on the whole mass of the carrier. Further, in the casewhere the carrier contains USY zeolite and alumina boria, it ispreferable that the proportion of USY zeolite to alumina boria to beblended (USY zeolite/alumina boria) be 0.03 to 1 in the mass ratio.Moreover, in the case where the carrier contains USY zeolite and silicaalumina, it is preferable that the proportion of USY zeolite to silicaalumina to be blended (USY zeolite/silica alumina) be 0.03 to 1 in themass ratio.

The binder is not particularly limited; alumina, silica, titania,magnesia are preferable, and alumina is more preferable. The amount ofthe binder to be blended is preferably 20 to 98% by mass, and morepreferably 30 to 96% by mass based on the whole mass of the carrier.

The temperature in firing the carrier composition is preferably in therange of 400 to 550° C., more preferably in the range of 470 to 530° C.,and still more preferably in the range of 490 to 530° C. Firing at sucha temperature can give sufficient solid acidity and mechanical strengthto the carrier.

Examples of Group 8 to Group 10 metals in the periodic table supportedby the carrier and having hydrogenation activity specifically includecobalt, nickel, rhodium, palladium, iridium, and platinum. Among these,metals selected from nickel, palladium, and platinum are preferably usedsingly or in combinations of two or more. These metals can be supportedon the carrier mentioned above by a standard method such as impregnationand ion exchange. The amount of the metal to be supported is notparticularly limited, and it is preferable that the total amount of themetal be 0.1 to 3.0% by mass based on the mass of the carrier. Here, theperiodic table of the elements refers to the long form of the periodictable of the elements based on the specification by IUPAC (theInternational Union of Pure and Applied Chemistry).

In the hydrocracker C6, the crude wax fraction and part of the uncrackedwax fraction (hydrocarbons having approximately C₂₁ or more) areconverted into hydrocarbons having approximately C₂₀ or less byhydrocracking; further, part thereof is converted into naphtha fraction(approximately C₅ to C₁₀) lighter than the target intermediate fraction(approximately C₁₁ to C₂₀) and further gaseous hydrocarbons having C₄ orless by excessive cracking. On the other hand, the crude wax fractionand part of the uncracked wax fraction are not subjected to sufficientlyhydrocracking, and become the uncracked wax fraction havingapproximately C₂₁ or more. The composition of the hydrocracking productis determined according to the hydrocracking catalyst to be used and thehydrocracking reaction condition. Here, the “hydrocracking product”refers to all hydrocracking products containing the uncracked waxfraction, unless otherwise specified. If the hydrocracking reactioncondition is tighter than necessary, the content of the uncracked waxfraction in the hydrocracking product is reduced while the light contentwhich weight is equal to or lighter than the naphtha fraction isincreased to reduce yield of the target intermediate fraction. On theother hand, if the hydrocracking reaction condition is milder thannecessary, the uncracked wax fraction is increased to reduce yield ofthe intermediate fraction. In the case where the ratio of the crackingproduct whose boiling point is 25 to 360° C. to the whole crackingproducts whose boiling point is not less than 25° C. ([mass of thecracking product whose boiling point is 25 to 360° C./mass of the wholecracking products whose boiling point is not less than 25° C.]×100(%))is defined as a “cracking rate,” the reaction condition is selected sothat the cracking rate may be usually 20 to 90%, preferably 30 to 80%,more preferably 45 to 70%.

In the hydrocracker C6, in parallel with the hydrocracking reaction, ahydrogenation isomerization reaction of normal paraffin that includesthe crude wax fraction and uncracked wax fraction or hydrocrackingproducts thereof progresses to produce isoparaffin. In the case wherethe hydrocracking product is used as the fuel oil base material,isoparaffin to be produced by the hydrogenation isomerization reactionis a component that makes contribution to improvement in fluidity at alow temperature, and it is preferable that the production rate be high.Further, removal of olefins and oxygen-containing compounds such asalcohols that are by-products of the FT synthesis reaction contained inthe crude wax fraction also progresses. Namely, olefins are convertedinto paraffin hydrocarbons by hydrogenation, and the oxygen-containingcompounds are converted into paraffin hydrocarbon and water byhydrodeoxidation.

The reaction condition in the hydrocracker C6 is not limited, and thefollowing reaction condition can be selected. Namely, examples of thereaction temperature include 180 to 400° C.; 200 to 370° C. ispreferable, 250 to 350° C. is more preferable, and 280 to 350° C. isparticularly preferable. At a reaction temperature more than 400° C.,not only does cracking into the light content tend to progress to reducethe yield of the intermediate fraction, but the product tends to becolored to limit use as the fuel oil base material. On the other hand,at a reaction temperature less than 180° C., not only does thehydrocracking reaction tend not to sufficiently progress to reduce theyield of the intermediate fraction, but production of isoparaffin by thehydrogenation isomerization reaction tends to be suppressed, and theoxygen-containing compounds such as alcohols tend not to be sufficientlyremoved to remain. Examples of the hydrogen partial pressure include 0.5to 12 MPa, and 1.0 to 5.0 MPa is preferable. At a hydrogen partialpressure less than 0.5 MPa, hydrocracking, hydrogenation isomerizationand the like tend not to sufficiently progress; on the other hand, at ahydrogen partial pressure more than 12 MPa, high pressure resistance isdemanded of the apparatus, and facility cost tends to be increased.Examples of the liquid hourly space velocity (LHSV) of the crude waxfraction and uncracked wax fraction include 0.1 to 10.0 h⁻¹, and 0.3 to3.5 h⁻¹ is preferable. At an LHSV less than 0.1 If% hydrocracking tendsto excessively progress, and productivity tends to be reduced; on theother hand, at an LHSV more than 10.0 h⁻¹, hydrocracking, hydrogenationisomerization and the like tend not to sufficiently progress. Examplesof the ratio of hydrogen/oil include 50 to 1000 NL/L, and 70 to 800 NL/Lis preferable. At a ratio of hydrogen/oil less than 50 NL/L,hydrocracking, hydrogenation isomerization and the like tend not tosufficiently progress; on the other hand, at a ratio of hydrogen/oilmore than 1000 NL/L, a large-sized hydrogen feeding apparatus or thelike tends to be needed.

In this example, the hydrocracking product and non-reacted hydrogen gasflowed from the hydrocracker C6 are cooled, and separated into gas andliquid at two stages by a gas liquid separator D8 and a gas liquidseparator D10, the relatively heavy liquid hydrocarbon containing theuncracked wax fraction is obtained from the gas liquid separator D8, andthe gas content mainly containing hydrogen gas and gaseous hydrocarbonshaving C₄ or less and the relatively light liquid hydrocarbon areobtained from the gas liquid separator D10. By such two-stage coolingand gas liquid separation, the occurrence of clogging of the lineaccompanied by solidification by rapid cooling of the uncracked waxfraction contained in the hydrocracking product, or the like can beprevented. The liquid hydrocarbons each obtained in the gas liquidseparator D8 and the gas liquid separator D10 merge with a line L32through a line L28 and a line L26, respectively. The gas contentseparated in a gas liquid separator D12 and mainly containing hydrogengas and gaseous hydrocarbon having C₄ or less is fed to the intermediatefraction hydrorefining apparatus C8 and the naphtha fractionhydrorefining apparatus C10 through a line (not shown) connecting thegas liquid separator D10 to the line L18 and the line L20, and hydrogengas is re-used.

Step S7

In Step S7, the crude intermediate fraction evacuated from the firstrectifying column C4 through the line L18, with the hydrogen gas fed bya feed line of the hydrogen gas connected to the line L18 (not shown),is heated to the temperature needed for hydrorefining of the crudeintermediate fraction by a heat exchanger H6 provided in the line L18,and fed to the intermediate fraction hydrorefining apparatus C8 to behydrorefined.

The type of the intermediate fraction hydrorefining apparatus C8 is notparticularly limited, and a fixed bed flow reactor filled with ahydrorefining catalyst is preferably used. The reactor may be singular,or a plurality of reactors may be provided in serial or in parallel.Moreover, the catalyst bed within the reactor may be singular or plural.

As the hydrorefining catalyst used in the intermediate fractionhydrorefining apparatus C8, catalysts usually used for hydrorefiningand/or hydrogenation isomerization in petroleum refining or the like,namely, the catalysts in which an active metal having hydrogenationability is supported by an inorganic carrier can be used.

As the active metal that forms the hydrorefining catalyst, one or moremetals selected from the group consisting of metals in

Groups 6, 8, 9, and 10 in the periodic table of the elements are used.Specific examples of these metals include noble metals such as platinum,palladium, rhodium, ruthenium, iridium, and osmium, or cobalt, nickel,molybdenum, tungsten, and iron; preferable are platinum, palladium,nickel, cobalt, molybdenum, and tungsten, and more preferable areplatinum and palladium. Moreover, two or more of these metals are alsopreferably used in combination; examples of a preferable combination inthis case include platinum-palladium, cobalt-molybdenum,nickel-molybdenum, nickel-cobalt-molybdenum, and nickel-tungsten.

Examples of the inorganic carrier that forms the hydrorefining catalystinclude metal oxides such as alumina, silica, titania, zirconia, andboria. These metal oxides may be used alone, or used as a mixture of twoor more thereof, or a composite metal oxide such as silica alumina,silica zirconia, alumina zirconia, and alumina boria. From the viewpointof efficiently progressing hydrogenation isomerization of normalparaffin at the same time of hydrorefining, it is preferable that theinorganic carrier be a composite metal oxide having solid acidity suchas silica alumina, silica zirconia, alumina zirconia, and alumina boria.Moreover, a small amount of zeolite may be contained in the inorganiccarrier. Further, in order to improve the moldability and mechanicalstrength of the carrier, a binder may be blended in the inorganiccarrier. Examples of a preferable binder include alumina, silica, andmagnesia.

In the case where the active metal is the noble metal mentioned above,it is preferable that the content of the active metal in thehydrorefining catalyst be approximately 0.1 to 3% by mass as the metalatom based on the mass of the carrier. Moreover, in the case where theactive metal is a metal other than the noble metal, it is preferablethat the content be approximately 2 to 50% by mass as metal oxide basedon the mass of the carrier. In the case where the content of the activemetal is less than the lower limit value, hydrorefining andhydrogenation isomerization tend not to sufficiently progress. On theother hand, in the case where the content of the active metal is morethan the upper limit value, dispersion of the active metal tends to bereduced to reduce the activity of the catalyst, and cost of the catalystis increased.

In hydrorefining of the crude intermediate fraction (normal paraffinhaving approximately C₁₁ to C₂₀ is a main component) in the intermediatefraction hydrorefining apparatus C8, olefins that are a by-product ofthe FT synthesis reaction contained in the crude intermediate fractionare hydrogenated to be converted into paraffin hydrocarbon. Moreover,the oxygen-containing compounds such as alcohols are converted intoparaffin hydrocarbon and water by hydrodeoxidation. Moreover, inparallel with the hydrorefining, the hydrogenation isomerizationreaction of normal paraffin that forms the crude intermediate fractionprogresses to produce isoparaftin. In the case where the intermediatefraction is used as the fuel oil base material, the isoparaffin producedby the hydrogenation isomerization reaction is a component that makescontribution to improvement in fluidity at a low temperature, and it ispreferable that the production rate be high.

The reaction condition in the intermediate fraction hydrorefiningapparatus C8 is not limited, and the following reaction condition can beselected. Namely, examples of the reaction temperature include 180 to400° C., 200 to 370° C. is preferable, 250 to 350° C. is morepreferable, and 280 to 350° C. is particularly preferable. At a reactiontemperature more than 400° C., cracking into the light content tends toprogress to reduce the yield of the intermediate fraction, and theproduct tends to be colored to limited use as fuel oil base material. Onthe other hand, at a reaction temperature less than 180° C., theoxygen-containing compounds such as alcohols tend not to sufficiently beremoved to remain, and production of isoparaffin by the hydrogenationisomerization reaction tends to be suppressed. Examples of the hydrogenpartial pressure include 0.5 to 12 MPa, and 1.0 to 5.0 MPa ispreferable. At a hydrogen partial pressure less than 0.5 MPa,hydrorefining and hydrogenation isomerization tend not to sufficientlyprogress; on the other hand, a hydrogen partial pressure more than 12MPa, high pressure resistance is demanded of the apparatus, and facilitycost tends to be increased. Examples of the liquid hourly space velocity(LHSV) of the crude intermediate fraction include 0.1 to 10.0 h⁻¹, and0.3 to 3.5 h⁻¹ is preferable. At an LHSV less than 0.1 h⁻¹, crackinginto the light content tends to progress to reduce the yield of theintermediate fraction, and productivity tends to be reduced; on theother hand, at an LHSV more than 10.0 h¹, hydrorefining andhydrogenation isomerization tend not to sufficiently progress. Examplesof the ratio of hydrogen/oil include 50 to 1000 NL/L, and 70 to 800 NL/Lis preferable. At a ratio of hydrogen/oil less than 50 NL/L,hydrorefining and hydrogenation isomerization tend not to sufficientlyprogress; on the other hand, at a ratio of hydrogen/oil more than 1000NL/L, a large-sized hydrogen feeding apparatus and the like tend to beneeded.

After the gas content mainly containing the non-reacted hydrogen gas isseparated in the gas liquid separator D12 to which a line L30 isconnected, an outflow oil of the intermediate fraction hydrorefiningapparatus C8 is transferred through the line L32 to merge with theliquid hydrocracking product of the wax fraction transferred by the lineL26. The gas content mainly containing hydrogen gas separated by the gasliquid separator D12 is fed to the hydrocracker C6, and re-used.

Step S8

In Step S8, the crude naphtha fraction evacuated from the firstrectifying column C4 by the line L20, with the hydrogen gas fed by afeed line of the hydrogen gas (not shown) connected to the line L20, isheated to the temperature needed for hydrorefining of the crude naphthafraction by a heat exchanger H8 installed in the line L20, and then fedto the naphtha fraction hydrorefining apparatus C10 to be hydrorefined.

The type of a naphtha fraction hydrorefining apparatus C10 is notparticularly limited, and a fixed bed flow reactor filled with ahydrorefining catalyst is preferably used. The reactor may be singular,or a plurality of reactors may be provided in serial or in parallel.Moreover, the catalyst bed within the reactor may be singular or plural.

The hydrorefining catalyst used for the naphtha fraction hydrorefiningapparatus 10 may be the same hydrorefining catalyst as that used forhydrorefining of the crude intermediate fraction.

In hydrorefining of the crude naphtha fraction (normal paraffin havingapproximately C₅ to C₁₀ is a principal component.) in the naphthafraction hydrorefining apparatus C10, unsaturated hydrocarbon containedin the crude naphtha fraction is converted into paraffin hydrocarbon byhydrogenation. Moreover, the oxygen-containing compounds contained inthe crude naphtha fraction such as alcohols are converted into paraffinhydrocarbon and water by hydrodeoxidation. In the naphtha fraction, thehydrogenation isomerization reaction does not progress much because thenumber of carbon atoms is small.

The reaction condition in the naphtha fraction hydrorefining apparatusC10 is not limited, and the same reaction condition as that in theintermediate fraction hydrorefining apparatus C8 mentioned above can beselected.

The outflow oil of the naphtha fraction hydrorefining apparatus C10 isfed through a line L34 to a gas liquid separator D14; in the gas liquidseparator D14, the outflow oil is separated into the gas content, inwhich hydrogen gas is a principal component, and liquid hydrocarbon. Theseparated gas content is fed to the hydrocracker C6, and hydrogen gascontained in this is re-used. On the other hand, the separated liquidhydrocarbon is transferred through the line L36 to the naphthastabilizer C14. Moreover, part of the liquid hydrocarbon is recycledthrough a line L48 to the line L20 upstream of the naphtha fractionhydrorefining apparatus C10. Because the amount of heat to be producedin hydrorefining of the crude naphtha fraction (hydrogenation of olefinsand hydrodeoxidation of alcohols and the like), part of the liquidhydrocarbon is recycled to the naphtha fraction hydrorefining apparatusC10, and the crude naphtha fraction is diluted; thereby, increase in thetemperature in the naphtha fraction hydrorefining apparatus C10 issuppressed.

In the naphtha stabilizer C14, the liquid hydrocarbon fed from thenaphtha fraction hydrorefining apparatus C10 and the second rectifyingcolumn C12 is fractionated to obtain refined naphtha with carbon atomsof C₅ to C₁₀ as a product. The refined naphtha is transferred from thecolumn bottom of the naphtha stabilizer C14 through a line L46 to astorage tank T8, and stored. On the other hand, from a line L50connected to the column top of the naphtha stabilizer C14, hydrocarbongas in which hydrocarbon with the number of carbon atoms of apredetermined number or less (C₄ or less) is a principal component isdischarged. Because the hydrocarbon gas is not a target product, thehydrocarbon gas is introduced into an external burning facility (notshown) to be burned, and then discharged into the air.

Step S9

In Step S9, the mixed oil comprising the liquid hydrocarbon obtainedfrom the outflow product from the hydrocracker C6 and the liquidhydrocarbon obtained from the outflow product from the intermediatefraction hydrorefining apparatus C8 is heated by a heat exchanger H10installed in the line L32, and fed to the second rectifying column C12to be fractionated into hydrocarbon having approximately C₁₀ or less, akerosene fraction, a light oil fraction, and a uncracked wax fraction.In the hydrocarbon having approximately C₁₀ or less, the boiling pointis lower than approximately 150° C.; the hydrocarbon is evacuated fromthe column top of the second rectifying column C12 by a line L44. In thekerosene fraction, the boiling point is approximately 150 to 250° C.;the kerosene fraction is evacuated from the central portion of thesecond rectifying column C12 by a line L42 to be stored in a storagetank T6. In the light oil fraction, the boiling point is approximately250 to 360° C.; the light oil fraction is evacuated from the lowerportion of the second rectifying column C12 by a line L40 to be storedin a storage tank T4. In the uncracked wax fraction, the boiling pointexceeds 360° C.; the uncracked wax fraction is evacuated from the columnbottom of the second rectifying column C12 to be recycled by the lineL38 to the line L12 upstream of the hydrocracker C6. The hydrocarbonhaving approximately C₁₀ or less evacuated from the column top of thesecond rectifying column C12 is fed by the line L44 and the L36 to thenaphtha stabilizer, and fractionated with the liquid hydrocarbon fedfrom the naphtha fraction hydrorefining apparatus C10.

As above, the suitable embodiment of the method for producing ahydrocarbon oil and a production system according to the presentinvention has been described, but the present invention will not bealways limited to the embodiment described above.

For example, in the embodiment, as the GTL process, natural gas is usedas the raw material for production of the synthesis gas, while anon-gaseous hydrocarbon raw material such as asphalt and a residue oilmay be used, for example. Moreover, in the embodiment, fractionationinto three fractions of the crude naphtha fraction, the crudeintermediate fraction, and the crude wax fraction is performed in thefirst rectifying column C4, and the crude naphtha fraction and the crudeintermediate fraction are hydrorefined in individual steps; however,fractionation into two fractions of a crude light fraction of the crudenaphtha fraction and the crude intermediate fraction in combination andthe crude wax fraction may be performed, and the crude light fractionmay be hydrorefined in one step. Moreover, in the embodiment, thekerosene fraction and the light oil fraction are fractionated asseparate fractions in the second rectifying column C12; however, thesemay be fractionated as one fraction (intermediate fraction).

As described in the embodiment above, part of the crude wax fractionflowed from the column bottom of the first rectifying column C4 andcontaining the catalyst fine powder may be transferred to thehydrocracker C6 without capturing and removal of the catalyst finepowder. In this case, the catalyst fine powder flowed into thehydrocracker C6 may cause the problem mentioned above such as reductionin activity of the hydrocracking catalyst filled in the hydrocracker C6.The catalyst fine powder, however, are captured and removed from atleast part of the crude wax fraction flowed from the column bottom ofthe first rectifying column C4 and containing the catalyst fine powderin the storage tank T2; accordingly, the amount of the catalyst finepowder to flow into the hydrocracker C6 can be reduced if the samecumulative amount of the oil to flow in the hydrocracker C6 is comparedwith the case where the catalyst fine powder is not captured andremoved. As a result, operation time until the problem described abovemanifests itself can be increased.

INDUSTRIAL APPLICABILITY

The present invention can provide a method for producing a hydrocarbonoil and a production system that can efficiently suppress the flow ofthe catalyst fine powder derived from the catalyst to be used for the FTsynthesis reaction into the reaction system in the upgrading step of theFT synthetic oil.

REFERENCE SIGNS LIST

T2 . . . Storage tank, C4 . . . First rectifying column, C6 . . .Hydrocracker, C8 . . . Intermediate fraction hydrorefining apparatus,C10 . . . Naphtha fraction hydrorefining apparatus, C12 . . . Secondrectifying column, L12, L16 . . . Bypass line, L14 a, L14 b . . .Transfer line, 100 . . . System for producing hydrocarbon oil.

What is claimed is:
 1. A system for producing a hydrocarbon oil,comprising: a Fischer-Tropsch synthesis reaction apparatus for obtaininga hydrocarbon oil containing a catalyst fine powder derived from acatalyst, the apparatus having a slurry bed reactor holding a slurrycontaining a liquid hydrocarbon and the catalyst suspended in the liquidhydrocarbon within the slurry bed reactor; a rectifying column forfractionating the hydrocarbon oil into at least one distilled oil and acolumn bottom oil; a hydrocracker for hydrocracking the column bottomoil; a bypass line connecting a column bottom of the rectifying columnto the hydrocracker; a transfer line branched from a branching point ofthe bypass line; and a storage tank that is connected to the transferline, and in which the catalyst fine powder is sedimented to a bottomthereof to be captured.
 2. The system for producing a hydrocarbon oilaccording to claim 1, wherein the storage tank is configured to suppressmovement of the catalyst fine powder sedimented to the bottom of thestorage tank in the bottom of the storage tank.